In our day to day life, we come across a common necessity of selecting any object from a group of given quantity of objects of various colors or representative colors or shades. Objects which conform to certain grading, it is highly desirable to grade any object where color of the object is of higher commercial value. Color grading is used widely to characterize various naturally occurring objects or artificially produced objects like precious stones, gems etc.
Objects having naturally-occurring color variations can be different agricultural products such as grains, different nuts, fruits, vegetables etc. or artificially produced objects such as processed food products and are graded according to their colors, length, cut size, and defect data, etc. are graded which is a very well known process using some sorting or grading machine. Generally, the objects to be graded are kept on the moving conveyor and past an optical grading system or inspection system where they are automatically graded or sorted and then collected according to some desired characteristic of the produce and these desired characteristics are most commonly, the color variation of objects along with other external characteristics. For color grading/sorting of different objects, this optical grading system is associated with color and intensity of light reflected from a single object based according to color and intensity variation. Therefore, the optical grading system should be capable to identify, inspect color variations significantly. With moving conveyor on which objects to be graded are placed are conveyed with high speed or variations in speed, variations in type of object to be graded based on size, shape, color, surface characteristics, the vibration and sometimes rolling of objects on the conveyor will cause variations in the viewing distance and viewing angle when the objects pass through the optical grading system, due to which there is great difficulty in producing consistent signals which leads to poor color grading and such poorly graded objects stand commercially less valuable due to the inefficiency of the current color grading systems to view the objects in detail to detect color variations, surface defects/damages etc. To overcome these shortcomings, few inventions have been developed to provide different optical grading systems. Incidentally, Patent Document 1 (U.S. Pat. No. 4,979,815) titled “Laser range imaging system based on projective geometry” discloses an apparatus and a method for producing a range image of an area of the surface of an object, by viewing illuminated light beam on the surface of the object. Here, by projecting a substantially planar beam of light onto the surface to illuminate the surface along a light stripe. The illuminated light beam is viewed and converted into an image generating the range image of the object. A three dimensional (3D) image of the object is formed by moving the object while it is scanned. By measuring only the top view and the profile view the volume estimation may also be inaccurate, especially when the objects have a very irregular shape. By using a planar beam of light situated above the moving object only the visible part of the object facing the capturing means can be detected, from which a two dimensional image will be formed. Parts of the object such as parts of the surface that is not in line of sight from the viewpoint of the capturing means as well as all the downwardly facing parts of the object will not be visible for the capturing means as will therefore appear as blanks in the captured image. This causes an increase in uncertainty in the measurement, and therefore the apparatus and the related method fails to provide accurate color grading. Patent Document 2 (U.S. Pat. No. 5,184,733) titled “Apparatus and method for determining the volume, form and weight of objects” which includes a line scan camera to record a top view of the object and simultaneously to record a profile view of the object through a mirror positioned on a fixed support at the side of a conveyor. From these data the width and the height of the object is determined. Accordingly, the composition image of the object consists of many cross-sections, with the width and the maximum thickness of the object being measured in each cross-section. By determining only the width and height of the object, the errors can be very high, especially when the object has irregular structure which leads to inefficient color grading of objects. In both Patent Document 1 and 2, the accuracy of the image getting from side views is not sufficient enough for effective color grading of objects.
Patent Document 3 (Chinese Patent Pub. No. CN103056111) titled “Prawns quality detecting and classifying device based on machine vision technology”, discloses a machine vision technology which includes a single camera fixed at the top end of a lighting box above the conveyor belt, and a white unsmooth coating is painted on inner walls of the lighting box. Light source illuminates upwards, and reflects to the surface of the prawn through the white coating of the inner walls so capturing only top views of object. A single camera and a light source to capture only one side of object fail to provide an accurate grade of object. For efficient color grading, object must be viewed clearly from all the sides to know even a smaller color defect.
Patent document 4 is our previously filed Patent application (WIPO Publication No. WO2015128872), titled “An improved machine for grading small sized irregular objects and a process thereof” discloses a grading machine comprising with imaging systems with multi-wavelength lighting system for surface property extraction of any small sized, irregular or uneven object of interest and also having multi-vision transparent tray assembly with transparent cups to accommodate one object in one cup. These imaging systems are programmed in such a way that they can see multiple sides of the single given object of a single cup, to decide the category of that object, but the disclosed grading machine lacks in deciding views and multi-reflectance due to lack of due to lack of mirrors/prisms or multiple programmable cameras for each object individually, therefore it suggests further tremendous scope in development of technology. Due to complexity involved in capturing multi-reflectance and multi-angle views of objects, even after using multiple cameras to view the object three dimensionally the current systems are unable to grade the objects of interest efficiently according to different external characteristics including size, shape, color variations, surface characteristics like surface defects/damages such as water marks, oil marks, surface properties or any other characteristics.
Accordingly, for further advancements in the existing optical grading system which is simple, easy to install in any grading system, and which deals with accurate, color grading of large range of objects with multi-reflection and multi-angle view based analysis of objects to effectively grade objects according to different external characteristics. Therefore, it would be highly desirable to provide a novel color based optical grading system with multi-reflectance and multi-angle views for grading accurately different types of objects in multiple grades in a single pass, which is simple, portable, and easy to install in any grading machine and also to provide a novel color based optical grading method for grading different types of objects rapidly and accurately into multiple grades in a single pass to increase the efficiency of any grading machine, thereby obviating all abovementioned shortcomings of the existing optical grading systems.